Synthesis and characterization of LRE_1+xBa_2-xCu₃O_y (LRE: Nd, Eu, Gd, NEG) superconductors: A low oxygen partial pressure (0.05% O₂+Ar)

We have investigated the effect of low oxygen partial pressure (pO₂ of 0.05%) on the microstructure and magnetic properties of NdBa₂Cu₃O_y, EuBa₂Cu₃O_y, GdBa₂Cu₃O_y, and (Nd, Eu, Gd)Ba₂Cu₃O_y. The heat treatment profiles for the melt processes were determined according to the peritectic decomposition temperature obtained by thermal analysis. All the samples showed relatively high T_c in the range of 93.6-96.1 K. Optical and scanning electron microscopy showed that in the Gd-123 matrix the secondary phase particles formed sub-micron-sized bundles. The scaling study of the normalized volume pinning forces showed that ΔT_c type pinning is dominant in all the samples. The Gd-123 sample exhibits the highest zero-field critical current density of 88 000 A cm^-2 at 77 K for the H ∥c-axis, while the highest secondary peak J_c of 65 000 A cm^-2 was achieved in Nd123 at 1 T and 77 K for the H ∥c-axis.